Radioisotope production

ABSTRACT

A radioisotope production apparatus comprising an electron source arranged to provide an electron beam. The electron source comprises an electron injector and an electron accelerator. The radioisotope production apparatus further comprises a target support structure configured to hold a target and a beam splitter arranged to direct the a first portion of the electron beam along a first path towards a first side of the target and to direct a second portion of the electron beam along a second path towards a second side of the target.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/770,688, 371(c) Date of Apr. 24, 2018, which isNational Stage Entry of International Application No. PCT/EP2016/076534,filed on Nov. 3, 2016, which claims priority to European PatentApplication 15193337.1, filed on Nov. 6, 2015, the entire contents ofall of which are incorporated herein by references.

FIELD

The present invention relates to radioisotope production apparatus andassociated methods. The present invention may be used in a systemcomprising a free electron laser and a radioisotope productionapparatus.

BACKGROUND

Radioisotopes are isotopes which are not stable. A radioisotope willdecay after a period of time by emitting a proton and/or neutron.Radioisotopes are used for medical diagnostics and for medicaltreatments, and are also used in industrial applications

The most commonly used medical radioisotope is Tc-99m (Technetium),which is used in diagnostic applications. Production of Tc-99m uses ahigh flux nuclear reactor. Highly enriched uranium, comprising a mixtureof U-238 and U-235 is bombarded with neutrons in the nuclear reactor.This causes some of the U-235 to undergo fission and to separate intoMo-99+Sn(×13)+neutrons. The Mo-99 is separated out from the otherfission products and shipped to a radiopharmacy. Mo-99 has a half-lifeof 66 hours and decays to Tc-99m. The Tc-99m has a half-life of only 6hours (which is useful for medical diagnostic techniques). At theradiopharmacy Tc-99m is separated from the Mo-99 and is then used formedical diagnostic techniques.

Mo-99 is widely used around the world to generate Tc-99m for medicaldiagnostic techniques. However, there are only a handful of high fluxnuclear reactors which can be used to generate Mo-99. Otherradioisotopes are also made using these high flux nuclear reactors. Allof the high flux nuclear reactors are over 40 years old and cannot beexpected to continue to operate indefinitely.

It may be considered desirable to provide an alternative radioisotopeproduction apparatus and associated methods and/or associated systems.

According to an aspect described herein there is provided a radioisotopeproduction apparatus comprising an electron source arranged to providean electron beam, the electron source comprising an electron injectorand an electron accelerator. The radioisotope production apparatusfurther comprises a target support structure configured to hold a targetand a beam splitter. The beam splitter is arranged to direct a firstportion of the electron beam along a first path towards a first side ofthe target and to direct a second portion of the electron beam along asecond path towards a second side of the target.

In this way, heat caused by the electron beam is better distributedthroughout the target.

The electron beam may comprise a plurality of pulses and the beamsplitter may be arranged to direct substantially half of the pulsesalong the first path and half of the pulses along the second path. Inthis way, each side of the target will see substantially half of thepulses of the electron beam. The beam splitter may comprise a deflector.

The target may comprise an electron target and a photon target. Theelectron target may be arranged to receive at least one of the first andsecond portions of the electron beam and to emit photons towards thephoton target.

The electron target may comprise a first part arranged to receive thefirst portion of the electron beam and a second part arranged to receivethe second portion of the electron beam. The first and second parts ofthe electron target may be disposed either side of the photon target.

The radioisotope production apparatus may further comprise a coolingapparatus arranged to provide a fluid coolant to the target. The coolingapparatus may be arranged to provide a liquid coolant to the electrontarget and to provide a gas coolant to the photon target. The gascoolant may be provided at a higher pressure than the liquid coolant.

According to a second aspect described herein, there is provided aradioisotope production apparatus comprising an electron source arrangedto provide an electron beam, the electron source comprising an electroninjector and an electron accelerator. The radioisotope productionapparatus further comprises a target support structure configured tohold a target and a first and a second electron beam distributionapparatus, together arranged to scan the electron beam over a surface ofthe target.

The first beam distribution apparatus may be a first deflector arrangedto sweep the electron beam through a predetermined angle towards thesecond electron beam distribution apparatus.

The second beam distribution apparatus may be a second deflectorarranged to deflect the sweeped electron beam such that it impactssubstantially telecentrically on the target. The second distributionapparatus may alternatively be a lens arranged to collimate the electronbeam.

The radioisotope production apparatus may further comprise a beamsplitter arranged to direct the a first portion of the electron beamalong a first path towards a first side of the target and to direct asecond portion of the electron beam along a second path towards a secondside of the target.

The first and second beam distribution apparatuses may be disposed alongthe first path.

The radioisotope production apparatus may further comprise third andfourth beam distribution apparatuses together arranged to scan theelectron beam over a further surface of the target, the third and fourthbeam distribution apparatuses disposed along the second path.

The target may comprise an electron target and a photon target. Theelectron target may be arranged to receive the electron beam from thesecond electron beam distribution apparatus and to emit photons towardsthe photon target. The electron target may comprise a first partarranged to receive the first portion of the electron beam from thefirst and second distribution apparatuses and a second part arranged toreceive the second portion of the electron beam from the third andfourth distribution apparatuses.

According to a third aspect described herein, there is provided aradioisotope production apparatus comprising an electron source arrangedto provide an electron beam, the electron source comprising an electroninjector and an electron accelerator. The radioisotope productionapparatus may further comprise an electron target support structureconfigured to hold an electron target to receive the electron beam as togenerate photons and a photon target support structure configured tohold a photon target for receipt of at least some of the photons.

The radioisotope production apparatus may be configured to inducerelative movement between the electron target and the electron beam.

The radioisotope production apparatus may further comprise an electronbeam distribution apparatus arranged to move the electron beam relativeto the electron target.

The electron beam distribution apparatus may comprise one or more beamdeflectors.

A beam deflector may be configured to scan the electron beam over thesurface of the electron target.

The electron beam distribution apparatus may comprise a lens. A lens maybe configured to collimate the electron beam.

The electron target support structure may be configured to move theelectron target relative to the electron beam. For example, the electrontarget support structure may be configured to rotate the electrontarget.

The electron target may be a liquid and the electron target supportstructure may be configured to cause the electron target to flow throughan electron beam target region.

The radioisotope production apparatus may further comprise a coolingapparatus arranged to provide a fluid coolant to the target. The coolingapparatus may be arranged to provide a liquid coolant to an electrontarget portion of the target and to provide a gas coolant to a photontarget portion of the target. The cooling apparatus may be arranged toprovide the gas coolant at a higher pressure than the liquid coolant.

The cooling apparatus may be arranged to provide a Helium coolant at apressure of approximately 70 bar to the photon target and to provide awater coolant at a pressure of approximately 1 bar to the electrontarget.

According to a fourth aspect described herein, there is provide aradioisotope production apparatus comprising an electron source arrangedto provide an electron beam, the electron source comprising an electroninjector and an electron accelerator. The radioisotope productionapparatus further comprises a chamber containing a target supportstructure configured to hold a target in a path of the electron beam anda window through which the electron beam enters the chamber. The windowmay comprise Silicon Carbide.

In this way, the apparatus provides a window that allows transmission ofthe electron beam and/or photons, is thermally stable and able towithstand pressure differences between the environment of the electronbeam and the chamber.

The window may be dome-shaped. The window may have a curvature ofbetween 85 mm to 4000 mm.

The window may be manufactured by chemical vapour deposition and thechamber may be chamber hermetically sealed.

According to a fifth aspect described herein, there is provided a methodof producing a radioisotope having a specific activity within a desiredrange. The method comprises generating a radioisotope using radioisotopeproduction apparatus. The radioisotope production apparatus comprises anelectron source arranged to provide an electron beam, the electronsource comprising an electron injector and an electron accelerator and atarget support structure configured to hold a target. The method furthercomprises physically, e.g. mechanically, separating at least one portionof the radioisotope having a specific activity within the desired range.

The method may further comprise perforating the target prior to exposingthe target to the electron beam to generate the radioisotope.

The radioisotope production apparatus may be a radioisotope productionapparatus according to any of the above described first to fourthaspects.

According to a sixth aspect described herein, there is provided a systemcomprising a radioisotope production apparatus according to any of thefirst to fourth aspects and a free electron laser comprising an energyrecovery electron accelerator and an undulator. The electron acceleratorof the radioisotope production apparatus is positioned to receive anelectron beam after it has been accelerated then decelerated by theenergy recovery electron accelerator, the electron accelerator of theradioisotope production apparatus being configured to accelerateelectrons of the electron beam to an energy of around 14 MeV or more forsubsequent delivery to the electron target of the radioisotopeproduction apparatus.

According to a seventh aspect described herein, there is provided atarget for use with a radioisotope production apparatus. The targetcomprises a plurality of spaced portions. The target is configured toexpand when the target is subjected to an electron beam such thatcontact between the plurality of portions is prevented.

The target may be configured to expand such that a gap or space betweenadjacent portions of the plurality of portions may be maintained.

The target may comprise a plurality of contact points at which adjacentportions of the plurality of portions are in contact. The target maycomprise a plurality of openings arranged to extend between at least twocontact points of the plurality of contact points.

The target may comprise a flexible or deformable target.

The target may comprise a lattice-type structure or a honeycombstructure.

The plurality of portions may comprise a plurality of target elements.The plurality of target elements may be arranged to form the target.Each target element may comprise a plurality of grooves orthrough-holes.

The plurality of portions may be concentrically arranged relative toeach other.

The plurality of portions may be arranged to form a helical or spiralstructure.

According to an eight aspect described herein, there is provided atarget for use with a radioisotope production apparatus. The target isconfigured to expand when the target is subjected to an electron beamsuch that flow of a coolant through the target is allowed or maintained.

The target may comprise a porous structure or material. For example, theporous structure or material may comprise a foam or sintered material.

According to a ninth aspect described herein, there is provided a targetarrangement for use with a radioisotope production apparatus comprisinga target and a target support structure. The target support structure isconfigured to move or rotate the target relative to an electron beam.

The target may be or comprise a target according to the seventh and/oreighth aspects.

The target support structure may be configured to move or rotate thetarget about a transverse axis or a longitudinal axis of the target.

The target arrangement may comprise a housing. The target arrangementmay comprise a window for transmission of the electron beam into thehousing.

The target support structure may be arrangeable or arranged in thehousing to move or rotate the target relative to the housing and thewindow.

The window may be arranged to surround the target. The target supportstructure may be configured to move or rotate the housing and windowwith the target.

According to a tenth aspect described herein, there is provided aradioisotope production apparatus comprising an electron source arrangedto provide an electron beam, the electron source comprising an electroninjector and an electron accelerator. The radioisotope productionapparatus comprises a target arrangement for arranging a target relativeto the electron beam and an electron beam focusing arrangementconfigured to focus the electron beam on the target.

The target arrangement may comprise a target arrangement according tothe ninth aspect.

According to an eleventh aspect described herein, there is provided atarget arrangement for use with a radioisotope production apparatuscomprising a target. The target comprises a plurality of spaced targetelements. The target arrangement comprises a target support structureconfigured to suspend a part of the plurality of target elements toallow expansion of the part of target elements in at least onedirection.

The plurality of target elements may be arranged to be staggered in atleast one direction of the target. The plurality of target elements maybe arranged to be in line or aligned in at least one other direction ofthe target.

The target support structure may comprise a plurality of supportelements. Each support element may be configured to suspend a portion ofthe plurality of target elements.

The target support structure may comprise a first portion for suspendingthe part of the plurality of target elements. The target supportstructure may comprise a second portion for supporting a free end ofanother part of the plurality of target elements.

A space between adjacent target elements of the plurality of targetelements may be selected to allow for dilation or expansion of thetarget elements in at least one other direction.

According to a twelfth aspect described herein, there is provided atarget for use with a radioisotope production apparatus. The targetcomprises a first material. The first material comprises a substratematerial for conversion into a radioisotope. The target comprises asecond material. The second material may be configured to retainconverted substrate material. The second material may be arranged orarrangeable in or with the first material to form the target.

The substrate material may comprise at least one of Dysposion-158(Dy-158), Radium-226 (Ra-226), Thorium (Th-228) and Nickel-64 (Ni-64).

The second material may comprise a plurality of particles. Each particlemay have a size or diameter of about 10 nm.

The second material may comprise at least one of graphene, carbon andmetal.

The second material may be suspended or dispersed in a substance orfluid, e.g. a liquid. The second material may comprise a colloid orcolloid solution.

According to a thirteenth aspect described herein, there is provided amethod of producing a radioisotope. The method comprises arranging atarget in a radioisotope production apparatus. The target comprises afirst material. The first material comprises a substrate material forconversion into a radioisotope. The target comprises a second material.The second material is configured to retain converted substratematerial. The second material is arranged or arrangeable in or with thefirst material to form the target. The method comprises irradiating thetarget with an electron beam. The electron beam is configured to causeconversion of a part of the substrate material into the radioisotope.The electron beam is configured to cause displacement of some of theconverted substrate material into the second material. The methodcomprises separating the converted substrate material from the secondmaterial.

The step of separating may comprise separating the second material fromthe first material, prior to separating the converted substrate materialfrom the second material.

According to a fourteenth aspect described herein, there is provided aradioisotope production apparatus comprising an electron source toprovide an electron beam, the electron source comprising an injector andan electron accelerator. The radioisotope production apparatus comprisesa chamber containing a target support structure configured to hold atarget in a path of the electron beam. The radioisotope productionapparatus comprises a separation element for separating the chamber fromthe electron source. The separation element comprises an aperturethrough which the electron beam enters the chamber.

The radioisotope production apparatus may comprise a shielding elementarranged between the separation element and the target supportstructure. The shielding element may comprise an aperture through whichthe electron beam passes to the target.

The aperture of the shielding element may be larger than the aperture ofthe separation element.

The radioisotope production apparatus may comprise a further separationelement. The further separation element may comprise a further aperturethrough which the beam passes towards the target.

The further aperture of the further separation element may of the samesize or of a different size than the aperture of the separation element.

The radioisotope production apparatus may comprise a cooling apparatus.The cooling apparatus may be arranged to provide a coolant to thetarget.

The separation element and/or further separation element is arranged inthe chamber such that flow of coolant is allowed through the apertureand/or further aperture towards the electron source.

Features of any given aspect of the invention may be combined withfeatures of other aspects of the invention.

Various aspects and features of the invention set out above or below maybe combined with various other aspects and features of the invention aswill be readily apparent to the skilled person.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings, in which:

FIG. 1 is a schematic illustration of a radioisotope productionapparatuses;

FIG. 2a is a schematic illustration of a target within a radioisotopeproduction apparatus;

FIG. 2b is a schematic illustration of a target comprising separateelectron and photon targets for a radioisotope production apparatus;

FIG. 3a is a schematic illustration of a target receiving radiation fromtwo sides;

FIG. 3b is a schematic illustration of a target including separateelectron and photon targets receiving radiation from two sides;

FIG. 4 is a schematic illustration of a radioisotope productionapparatus comprising beam distributing apparatuses;

FIGS. 5, 6 a, 6 b and 7 are schematic illustrations of dynamic electrontarget arrangements for a radioisotope production apparatus;

FIG. 8 is a schematic illustration of an electron target arrangement fora radioisotope production apparatus utilizing a liquid electron target;

FIG. 9 is a schematic illustration of a radioisotope produced inaccordance with a described arrangement;

FIG. 10 is a schematic illustration of part of a system comprising afree electron laser and a radioisotope production apparatus according toan embodiment of the invention;

FIGS. 11a to 11h are schematic illustrations of a target for aradioisotope production apparatus;

FIGS. 12a and 12b are schematic illustration of a target arrangement fora radioisotope production apparatus;

FIG. 13a is a schematic illustration of a target arrangement for aradioisotope production apparatus comprising a housing and window;

FIG. 13b is a schematic illustration of a target arrangement for aradioisotope production apparatus comprising a moveable target;

FIG. 13c is a schematic illustration of a target arrangement for aradioisotope production apparatus comprising a moveable housing, windowand target;

FIGS. 14a and 14b are schematic illustrations of an electron targetarrangements for a radioisotope production apparatus comprising anelectron beam focusing arrangement;

FIGS. 15a to 15c a schematic illustration of a target for a radioisotopeproduction apparatus;

FIGS. 16a to 16e are schematic illustrations of the process steps of amethod for producing a radioisotope;

FIG. 17a is a chart illustrating converted substrate materialimplantation into a second material;

FIG. 17b is a chart illustrating a distribution of converted material ina second material;

FIG. 17c is a nuclides chart illustrating an isotope distribution;

FIG. 18 is a schematic illustration of a target arrangement comprising aseparation element, which comprises an aperture;

FIG. 19 is a schematic illustration of a target arrangement comprising ashielding element, which comprises an aperture;

FIGS. 20a to 20c are schematic illustrations of coolant flow supply andextraction in parts of the target arrangement of FIG. 18; and

FIG. 21 is a schematic illustration of a target arrangement comprising afurther separation element, which comprises a further aperture.

Generally herein, the same reference numerals within the Figures torefer to the same or equivalent features.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a radioisotope production apparatus. Theradioisotope production apparatus RI comprises an electron injector 10and an electron accelerator 20 in the form of a linear accelerator. Theelectron injector 10 is arranged to produce a bunched electron beam andcomprises an electron source (for example a photo-cathode which isilluminated by a pulsed laser beam or a thermionic emission source) anda booster which provides an accelerating electric field. Theaccelerating electric field provided by the booster may for exampleaccelerate the electrons of the electron beam to an energy of around 10MeV.

Electrons in the electron beam E may be steered to the linearaccelerator 20 by magnets (not shown). The linear accelerator 20accelerates the electron beam E. In an example, the linear accelerator20 may comprise a plurality of radio frequency cavities which areaxially spaced, and one or more radio frequency power sources which areoperable to control the electromagnetic fields along the common axis asbunches of electrons pass between them so as to accelerate each bunch ofelectrons. The cavities may be superconducting radio frequency cavities.Advantageously, this allows: relatively large electromagnetic fields tobe applied at high duty cycles; larger beam apertures, resulting infewer losses due to wakefields; and for the fraction of radio frequencyenergy that is transmitted to the beam (as opposed to dissipated throughthe cavity walls) to be increased. Alternatively, the cavities may beconventionally conducting (i.e. not superconducting), and may be formedfrom, for example, copper. Other types of linear accelerators may beused such as, for example, laser wake-field accelerators or inverse freeelectron laser accelerators.

Although the linear accelerator 20 is depicted as lying along a singleaxis in FIG. 1, the linear accelerator may comprise modules which do notlie on a single axis. For example, a bend may be present between somelinear accelerator modules and other linear accelerator modules.

The linear accelerator 20 may, for example, accelerate electrons to anenergy of around 14 MeV or more. The linear accelerator may accelerateelectrons to an energy of around 30 MeV or more (e.g. up to around 45MeV). It may be beneficial not to accelerate the electrons to an energygreater than a predetermined desired amount (for example, 60 MeV)because at certain energies large quantities of unwanted products otherthan the desired radioisotope may be generated. In an embodiment, thelinear accelerator 130 a may accelerate electrons to an energy of around35 MeV.

The radioisotope production apparatus RI further comprises a target 30which is configured to receive the electrons and to use the electrons toconvert a source material into a radioisotope. The target 30 may beMo-100 (Mo-100 is a stable and naturally occurring isotope of Mo) whichis to be converted into Mo-99 via photon induced neutron emission. Themechanism via which the photons are generated is Bremsstrahlungradiation (in English: braking radiation) generated as a result of theelectrons hitting the target 30. The energy of the photons generated inthis manner may, for example, be greater than 100 keV, may be greaterthan 1 MeV, and may be greater than 10 MeV. The photons may be describedas very hard X-rays.

This reaction has a threshold energy of 8.29 MeV, and thus will notoccur if photons incident upon the photon target have an energy lessthan 8.29 MeV. The reaction has a cross-section which peaks at around 14MeV (the reaction cross-section is indicative of the chances of thereaction being induced by a photon with a given energy). In other words,the reaction has a resonance peak at around 14 MeV. Therefore, in anembodiment photons with an energy of around 14 MeV or more may be usedto convert a Mo-100 photon target into Mo-99.

The energy of the photons generated has an upper limit which is set bythe energy of the electrons in the electron beam E. The photons willhave a distribution of energies, but the upper limit of thatdistribution will not extend beyond the energy of the electrons in theelectron beam. Thus, in an embodiment used to convert a Mo-100 photontarget into Mo-99 the electron beam will have an energy of at least 8.29MeV. In an embodiment the electron beam E may have an energy of around14 MeV or more.

As the energy of the electron beam is increased, more photons withenergies sufficient to cause the desired reaction will be generated (forthe same current of electrons). For example, as noted above Mo-99generation has a cross-section which peaks at around 14 MeV. If theelectron beam E has an energy of around 28 MeV then each electron maygenerate two photons with an energy of around 14 MeV, thereby increasingconversion of the photon target to Mo-99. However, as the energy of theelectron beam is increased photons with higher energies will induceother unwanted reactions. For example, photon induced emission of aneutron and a proton has a threshold energy of 18 MeV. This reaction isnot desired because it does not generate Mo-99 but instead generates anunwanted reaction product.

In general, the selection of the energy of the electron beam (and hencethe maximum energy of the photons) may be based on a comparison betweenthe yield of wanted products (e.g. Mo-99) and the yield of unwantedproducts. In an embodiment, the electron beam may have an energy ofaround 14 MeV or more. The electron beam E may for example have anenergy of around 30 MeV or more (e.g. up to around 45 MeV). This rangeof electron beam energies may provide good productivity of photons withenergies around the reaction resonance peak of 14 MeV. In otherembodiments, however, the electron beam may have other energies. Forexample, the electron beam may have an energy of 60 MeV as electrons atthis energy may be capable of causing multiple reactions and therebyincreasing the yield.

FIG. 2a schematically depicts an example arrangement of the target 30.In FIG. 2a , the target 30 comprises a plurality of plates 32 of Mo-100supported by a support 31. As described above, when electrons in theelectron beam E are incident on the plates 32, photons are emitted. Thephotons emitted from the target 30 are schematically depicted by wavylines γ in FIG. 2a . When a photon γ is incident upon a Mo-100 nucleusit causes a photonuclear reaction via which a neutron is ejected fromthe nucleus. The Mo-100 atom is thereby converted to an Mo-99 atom. Inthe arrangement of FIG. 2a , the plates 32 may be considered to be bothan electron target and a photon target.

The target 30 may receive photons γ for a period of time, during whichthe proportion of Mo-99 in the target 30 increases and the proportion ofMo-100 in the target decreases. The target 30 is then removed from theradioisotope production apparatus RI for processing and transportationto a radiopharmacy. Tc-99, which is the decay product of Mo-99, isextracted and used in medical diagnostic applications.

FIG. 2b schematically depicts an alternative example arrangement of thetarget 30. In FIG. 2b , a target 30 further comprises a separateelectron target 34. Where a separate electron target is provided, thetarget plates 32 may be considered to be a photon target. The electrontarget 34 may, for example, be formed from tungsten, tantalum or someother material which will decelerate the electrons and generate photons.The electron target 34, may, however, be formed from the same materialas a photon target (e.g. Mo-100). The electron target is held by asupport structure 33.

Although the target 32 shown in FIG. 2 comprises three plates, thetarget may comprise any suitable number of plates. Although thedescribed target comprises Mo-100, the photon target may comprise anysuitable material. Similarly, the material of the target may be providedin any suitable shape and/or configuration. Shielding may be providedaround target 30 (e.g. lead shielding).

Although the electron target 34 of FIG. 2b is depicted as a single blockof material, it may be provided as a plurality of plates. The plates mayfor example have a construction which corresponds to the construction ofthe target plates 32 described above. Similarly, the support structure33 may be configured to hold a plurality of electron target plates.

The electron target 34 and the target plates 32 may be provided inconduits through which coolant fluid is flowed, as described furtherbelow.

Referring again to FIG. 1, the radioisotope production apparatus RIfurther comprises an electron beam splitter 40. The electron beamsplitter is arranged to split the electron beam E along two propagationpaths: a first propagation path towards one side of the target 30 and asecond propagation path towards an opposite side of the target 30.Magnets (not shown) may be provided to steer the electron beam E alongeach of the propagation path. As will be understood by those skilled inthe art, the electron beam E is what may be referred to as a pulsetrain. The electron beam splitter 40 is arranged to direct a portion ofthe pulses along the first path and a portion of the pulses along thesecond path. For example, 50% of the pulses in the electron beam E maybe sent along the first path, and 50% of the pulses sent along thesecond path. It will be appreciated, however, that any ratio of pulses(between the two propagation paths) may be used.

The electron beam splitter 40 may be implemented using any appropriatemeans and may be, for example a deflector (e.g. a kicker) utilizingmagnetic or electrostatic deflection. The splitting may be done at asufficiently high frequency that the thermal load is distributedsubstantially evenly on each side of the target 30. In some embodiments,pulses may be skipped within the electron beam E to allow time forswitching between pulses. By way of example, if pulses are generated at650 MHz, then 1000 pulses may be skipped every 10 milliseconds, leavingapproximately 1.5 microseconds for the beam splitter 40 to switch thepropagation path of the electron beam E.

FIG. 3a schematically illustrates the electron beam E received at eachside of the target 30. FIG. 3b schematically illustrates an arrangementof the target 30 where separate electron targets are provided. In FIG.3b , the target 30 comprises two electron targets 34 a, 34 b disposed atrespective sides of the target plates 32 and supported by respectivesupport structures 33 a, 33 b. Each electron target 34 a, 34 b isarranged to receive a portion of the electron beam E and to emit photonstowards either side of the target plates 32.

By distributing the headload more uniformly across the target 30, thetotal temperature generated at the target should be lower, therebyeasing and simplifying cooling requirements.

FIG. 4 schematically illustrates an alternative arrangement of aradioisotope production apparatus RI. In FIG. 4, a plurality of electronbeam distribution apparatuses are provided to distribute the electronbeam E over a face of the target 30. Generally, the electron beamdistribution apparatuses may be provided in the form of either, or acombination of deflectors and/or magnets, such as quadrupoles.

In the depicted example embodiment of FIG. 4, a first electron beamdistribution apparatus is provided in the form of a deflector 50disposed in the path of the electron beam E and configured to sweep theelectron beam E through an angle. In the particular example of FIG. 4,the deflector 50 is configured to sweep the electron beam E over thesurface of a second electron beam distribution apparatus. This may beachieved by applying a continuously varying voltage to plates of thedeflector 50. The second electron beam distribution apparatus may takethe form of a second deflector 60 arranged to deflect the electron beamE such that it impacts telecentrically on the surface of the target 30.In other embodiments, the second electron distribution apparatus 60 maytake the form of a lens used to collimate the electron beam E.Collimation of the electron beam E is useful because a divergingelectron beam would increase the divergence of photons generated. Thiswould in turn require larger targets in order to collect the photons,which would reduce the specific activity of Mo-99 (or otherradioisotope) generated at the targets. The lens may, for example, beformed from magnets, and may be a multipole (e.g. quadrupoles,hexapoles, octupoles) lens.

Together, the first and second distribution apparatus cause the electronbeam E to be distributed across a larger area of the target 30, therebydistributing the thermal load and consequently reducing coolingrequirements. Further, where a lens is used as the second electron beamdistribution apparatus 60, the strength of the lens may be dynamicallyadjusted to obtain a desired focal point of the electron beam E. Bymoving the focal point further downstream, it is possible to increasethe quantity of photons generated but at the expense of a higher thermalload on the irradiated portion of the target 30.

It will be appreciated that other arrangements of distributionapparatuses may be used. For example, in other embodiments, the firstdistribution apparatus may be provided in the form of a lens arranged todefocus and therefore enlarge the electron beam E to desired dimensionsat the second distribution apparatus 60. Generally, any combination ofstatic electron beam distribution apparatuses (e.g. lenses) and dynamicelectron beam distribution apparatuses (e.g. deflectors) may be used.

FIG. 5 schematically illustrates a target arrangement 70, which may beused with a radioisotope production apparatus. The target 70 comprisesan electron target 71 held by a support structure (not shown) and aphoton target 72 held by a support structure (not shown). The electrontarget 71 is separated from the photon target 72 via a window 73 throughwhich photonic radiation can pass. The targets 71, 72 are mounted withina housing 74. The housing 74 comprises a window 75 through which anelectron beam is directed towards the electron target 71 as describedabove.

The housing 74 and the window 73 together define two chambers, isolatedfrom one another: a first chamber 76 containing the electron target 71and a second chamber 77 containing the photon target 72. By isolatingeach of the chambers 76, 77, each of the electron target 71 and thephoton target 72 may be cooled separately. In this way, the electrontarget 71 may be subject to more effective cooling than can be appliedto the photon target 72. For example, where the photon target 72 isMo-100, this may prevent liquid cooling due to the solubility of Mo-100in a liquid coolant. However, as described above, the electron target 71may be made from a different material, such as Tungsten or Tantalumwhich would not be soluble in a liquid coolant. As such, it may bedesirable to cool the electron target with a liquid coolant whilecooling the photon target with a gas coolant. In the depicted example,the chamber 76 is cooled by a flow of water 76 a, while the photontarget 72 is cooled by a flow of helium (He) 77 a. In some embodiments,the coolants used to cool the photon target 72 and the electron target71 may be at different pressures. For example, as the cooling propertiesof flowing He are relatively poor in comparison to the coolingproperties of flowing water, the coolant supplied to the photon targetmay be supplied at a higher pressure. By way of example, in the targetarrangement 70 of FIG. 5, the water coolant 76 a may be supplied at apressure of 1 bar (100 kPa), while the helium coolant 77 a may besupplied at a pressure of 70 bar (7000 kPa).

Either or both of the windows 73, 75 may be constructed from, forexample, a thin layer of Silicon Carbide, or other suitable material. Itwill be appreciated that the windows should allow transmission of theelectron beam E and/or photons, be thermally stable and able towithstand pressure differences between the environment of the electronbeam (which may be vacuum) and the pressure differences between thefirst and second chambers 76, 77.

As indicated above, in some embodiments, a window is provided toseparate the photon target from either the vacuum in which the electronbeam is generated (e.g. where no separate electron target is provided)or the electron target (e.g. where a separate electron target isprovided). In some embodiments, the window which separates the photontarget from other areas may be dome-shaped so as to better withstand thepressure differential between the chamber housing the photon target andthe adjacent area. For example, with reference to FIG. 5, the window 73may be dome shaped to better withstand the 69 bar pressure differentialbetween the chambers 76, 77 while remaining sufficiently thin (asmeasured in the direction of propagation of the electron beam E to allowphotons to pass through the window 73 in sufficient quantities to impactthe photon target 72.

Similarly, where the photon target is adjacent the vacuum through whichthe electron beam E propagates, a pressure differential of, for example,70 bar may be present (where as described above, for example, Hydrogengas cooling is provided at a pressure of 70 bar). As such, the windowseparating the photon target with the vacuum may be dome shaped. Suchdome-shaped windows may be manufactured using chemical vapour deposition(CVD) of SiC, for example. In order to ensure resilience to forcesacting upon the windows, the windows may have a curvature of between 85to 4000 mm. Such a CVD-SiC dome-shaped window would be suitable forhermetic sealing, able to withstand high temperatures, conduct currentsand cope with the pressure difference between different areas of thetarget.

FIGS. 6a, 6b schematically depict a dynamic electron target arrangement80 according to an embodiment described herein. FIG. 6a depicts aside-view of the arrangement 80 (in a plane parallel to the direction ofpropagation of the electron beam E) while FIG. 6b depicts thearrangement 80 in a plane perpendicular to the direction of propagationof the electron beam E. The arrangement 80 comprises an electron target81, which, while depicted as a plurality of circular plates in FIGS. 6a,6b , may take any appropriate form as described above. For example, theelectron target 81 may comprise a plurality of plates of any shape, suchas rectangular plates.

The electron target 81 is configured to be rotated about an axis A-Adepicted as being at a center-point of the electron target 81. Forexample, the electron target 81 may be mounted on an axle defining theaxis A-A and suitable actuators may be provided to rotate the axle andthereby the electron target 81. It will be appreciated, however, thatthe electron target 81 may be caused to rotate about the axis A-A in anysuitable manner. Further, it is to be understood that the axis A-A neednot be centrally disposed within the electron target 81.

During use, the electron target 81 is rotated about the axis A-A suchthat a different portion of the target 81 is exposed to the electronbeam E at different times during an exposure. In this way, the heatimparted to the electron target 81 is distributed more uniformly overthe surface of the electron target 81, thereby reducing the cooling. Inother embodiments, the electron beam E may be moved over the surface ofthe target 81 target without the need to rotate the 81.

FIG. 7 depicts an alternative dynamic electron target arrangement 90 inwhich an electron target 91 comprises a plurality of rectangular platesarranged cylindrically around an axis B-B. As in the arrangement 80, theelectron target 91 is configured to be rotated about the axis B-B so asto expose different ones of the plates forming the electron target 91(or simply different portions of the electron target 91 where theelectron target 91 does not comprise a plurality of plates) to theelectron beam E. A pipe 92 surrounds the electron target 91 and providesa conduit for a coolant (e.g., water) to be sent through the electrontarget 91.

FIG. 8 schematically depicts an alternative dynamic electron targetarrangement 100 in which an electron target is provided in the form of a“curtain” of liquid through which the electron beam E is directed. InFIG. 8, an electron target reservoir 101 a is connected to an electrontarget trap 101 b via a supply pipe 102. The electron target reservoir101 a supplies (e.g. through the action of a pump) an electron target103 in the form of a liquid to the supply pipe 102 through which theelectron target 103 flows to the electron target reservoir 101 b. Theelectron beam E is directed towards the electron target 103 flowingthrough the supply pipe 102. The electron target 103 may be, forexample, PbBi or Hg. The electron target may be recirculated from theelectron target trap 101 b to the electron target reservoir 101 a viarecirculation pipes (not shown) and may be cooled during recirculation.By providing a flowing electron target 103 in the form of a liquid, theeffectively surface area of the electron target is increased, therebyimproving distribution of the heat load imparted to the electron target103 by the electron beam E. Additionally, the flow of the electrontarget 103 is such that heat is automatically removed from the vicinityof the electron beam E.

In an alternative arrangement Lead-Bismuth Eutectic (LBE) may be used asboth the electron target and a coolant liquid. LBE provides an advantagein that it has a higher boiling point than other coolant liquids (e.g.water). Other suitable liquids may be used as both the electron targetand a coolant liquid.

In an embodiment, a bearing is provided between the electron target 103and the other surfaces within the arrangement 100. For example, abearing may be provided in the form of a curtain of water between theliquid electron target 103 and other surfaces of the arrangement 100.

FIG. 9 schematically illustrates a photon target 110 in the form of asquare plate of, for example, Mo-100. The photon target 110 may be, forexample, a combined photon and electron target, or a separate photontarget, as discussed above. In the depiction of FIG. 9, the photontarget 110 has been processed to create perforations 111 to define acentral portion 112 and an outer portion 113 of the photon target 110.Generally, the Specific Activity of a photon target will vary radially,with a central portion having a higher Specific Activity than an outerportion. Furthermore, some applications demand or prefer radioisotopeshaving particular Specific Activities. As such, by separating the photontarget 110 into a plurality of portions, the different regions can beprovided to different parties for different applications. Theperforations 111 in the photon target 110 allow easy separation of theradial portions 112, 113 but it will be recognized from the above thatsuch perforations are not an essential feature of the embodiment. Othermethods to separate portions of the photon target, either before orafter exposure to the electron beam E, may be used, such as, forexample, presses, cutting, etc. as will be readily apparent to theskilled person.

FIG. 10 schematically shows an example of a system which comprises afree electron laser FEL and radioisotope production apparatus RIa-c. Thefree electron laser FEL is capable of generating an EUV radiation beamBFEL which is sufficiently powerful to supply a plurality oflithographic apparatus LA1-n with EUV radiation beams that may be usedto project patterns onto substrates.

The free electron laser FEL comprises two electron injectors 121 a,b, alinear accelerator 122, an undulator 124 and a beam dump 150. The freeelectron laser may also comprise a bunch compressor (not illustrated).The system in FIG. 10 can be switched between different modes ofoperation in which an electron beam E follows different paths. In theillustrated mode the electron beam E is depicted by a solid line, withalternative electron beam paths being depicted by a dashed line.

In the depicted mode of operation the second electron injector 21 bprovides an electron beam E which is used by the free electron laser togenerate an EUV radiation beam BFEL. The first electron injector 21 aprovides an electric beam EI which is used to generate radioisotopes asdescribed above.

Following acceleration by the linear accelerator 122 the electron beam Eis steered to the undulator 24 by magnets (not shown). Optionally, theelectron beam E may pass through a bunch compressor (not shown),disposed between the linear accelerator 122 and the undulator 24. Thebunch compressor may be configured to spatially compress existingbunches of electrons in the electron beam E.

The electron beam E then passes through the undulator 24. Generally, theundulator 24 comprises a plurality of modules. Each module comprises aperiodic magnet structure, which is operable to produce a periodicmagnetic field and is arranged so as to guide the electron beam Eproduced by the electron injector 121 a,b and linear accelerator 122along a periodic path within that module. The periodic magnetic fieldproduced by each undulator module causes the electrons to follow anoscillating path about a central axis. As a result, within eachundulator module, the electrons radiate electromagnetic radiationgenerally in the direction of the central axis of that undulator module.The radiated electromagnetic radiation forms a beam BFEL of EUVradiation which is passed to lithographic apparatus LA1-n and is used bythose lithographic apparatus to project patterns onto substrates.

The path followed by the electrons may be sinusoidal and planar, withthe electrons periodically traversing the central axis. Alternatively,the path may be helical, with the electrons rotating about the centralaxis. The type of oscillating path may affect the polarization ofradiation emitted by the free electron laser. For example, a freeelectron laser which causes the electrons to propagate along a helicalpath may emit elliptically polarized radiation, which may be desirablefor exposure of a substrate W by some lithographic apparatus.

As electrons move through each undulator module, they interact with theelectric field of the radiation, exchanging energy with the radiation.In general the amount of energy exchanged between the electrons and theradiation will oscillate rapidly unless conditions are close to aresonance condition. Under resonance conditions, the interaction betweenthe electrons and the radiation causes the electrons to bunch togetherinto microbunches, modulated at the wavelength of radiation within theundulator, and coherent emission of radiation along the central axis isstimulated. The resonance condition may be given by:

$\begin{matrix}{{\lambda_{em} = {\frac{\lambda_{u}}{2\gamma^{2}}\left( {1 + \frac{K^{2}}{A}} \right)}},} & (1)\end{matrix}$

where λ_(em) is the wavelength of the radiation, λ_(u) is the undulatorperiod for the undulator module that the electrons are propagatingthrough, γ is the Lorentz factor of the electrons and K is the undulatorparameter. A is dependent upon the geometry of the undulator 24: for ahelical undulator that produces circularly polarized radiation A=1, fora planar undulator A=2, and for a helical undulator which produceselliptically polarized radiation (that is neither circularly polarizednor linearly polarized) 1<A<2. In practice, each bunch of electrons willhave a spread of energies although this spread may be minimized as faras possible (by producing an electron beam E with low emittance). Theundulator parameter K is typically approximately 1 and is given by:

$\begin{matrix}{{K = \frac{q\;\lambda_{u}B_{0}}{2\pi\;{mc}}},} & (2)\end{matrix}$

where q and m are, respectively, the electric charge and mass of theelectrons, Bo is the amplitude of the periodic magnetic field, and c isthe speed of light.

The resonant wavelength λ_(em) is equal to the first harmonic wavelengthspontaneously radiated by electrons moving through each undulatormodule. The free electron laser FEL may operate in self-amplifiedspontaneous emission (SASE) mode. Operation in SASE mode may require alow energy spread of the electron bunches in the electron beam E beforeit enters each undulator module. Alternatively, the free electron laserFEL may comprise a seed radiation source, which may be amplified bystimulated emission within the undulator 24. The free electron laser FELmay operate as a recirculating amplifier free electron laser (RAFEL),wherein a portion of the radiation generated by the free electron laserFEL is used to seed further generation of radiation.

The electron beam E which exits the undulator 124 is steered by magnets(not shown) back into the linear accelerator 122. The electron beam Eenters the linear accelerator 122 with a phase difference of 180 degreesrelative to the electron beam produced by the electron injector 121 a,b.The RF fields in the linear accelerator therefore serve to deceleratethe electrons which are output from the undulator 24 and to accelerateelectrons output from the electron injector 121 a,b. As the electronsdecelerate in the linear accelerator 122 some of their energy istransferred to the RF fields in the linear accelerator 122. Energy fromthe decelerating electrons is therefore recovered by the linearaccelerator 122 and is used to accelerate the electron beam E outputfrom the electron injector 121. Such an arrangement is known as anenergy recovery linear accelerator (ERL).

After deceleration by the linear accelerator 122, the electron beamE_(R) is absorbed by a beam dump 150. The beam dump 150 may comprise asufficient quantity of material to absorb the electron beam E_(R). Thematerial may have a threshold energy for induction of radioactivity.Electrons entering the beam dump 150 with an energy below the thresholdenergy may produce only gamma ray showers but will not induce anysignificant level of radioactivity. The material may have a highthreshold energy for induction of radioactivity by electron impact. Forexample, the beam dump 150 may comprise aluminium (Al), which has athreshold energy of around 17 MeV. The energy of electrons of theelectron beam E after leaving the linear accelerator 122 may be lessthan 17 MeV (it may for example be around 10 MeV), and thus may be belowthe threshold energy of the beam dump 150. This removes, or at leastreduces, the need to remove and dispose of radioactive waste from thebeam dump 150.

In addition to comprising a free electron laser FEL and lithographicapparatus LA_(1-n), the system depicted in FIG. 1 further comprisesradioisotope production apparatus RI_(a-c). Three radioisotopeproduction apparatus RI_(a-c) are depicted, each of which has the samegeneral configuration. In particular, each radioisotope productionapparatus RI_(a-c) comprises a linear accelerator 130 _(a-c) and atarget arrangement 140 _(a-c). Additionally, it is to be understood thatthe radioisotope production apparatus RI_(a-c) may comprise or utilizeany of the arrangements and features described above with reference toFIGS. 1 to 9.

Generally, referring again to FIG. 10, production of a radioisotopeusing the first radioisotope production apparatus RI_(a) is performedwhen the electron beam E_(I) generated by the first electron injector 21a is not being used by the free electron laser FEL to generate an EUVradiation beam B_(FEL). A deflector 131 directs the electron beam E_(I)towards the first radioisotope production apparatus RI_(a). The secondelectron injector 121 b is operable to provide an electron beam E to thefree electron laser FEL during this time. A deflector 132 provided afterthe second electron injector 121 b does not direct the electron beam Etowards the second radioisotope production apparatus, but instead allowsthe electron beam to travel to the linear accelerator 122. The twoelectron injectors 121 a,b are operating simultaneously, the firstelectron injector 121 a providing an electron beam which is used togenerate radioisotopes and the second electron injector 121 b providingan electron beam which is used by the free electron laser FEL togenerate an EUV radiation beam B_(FEL).

The second radioisotope production apparatus RI_(b) has the same generalconfiguration as the first radioisotope production apparatus RI_(a) andthus comprises a linear accelerator 130 b and a target 140 b. When thesecond electron injector 121 b is providing an electron beam used by theradioisotope production apparatus RI_(b) to generate radioisotopes, thefirst electron injector 121 a provides an electron beam used by the freeelectron laser FEL to generate an EUV radiation beam B_(FEL). The pathstravelled by electron beams E are thus opposite to those depicted inFIG. 10. Switching of the electron beam paths is achieved by switchingthe configurations of the deflectors 131, 132. The first deflector 131no longer directs the electron beam generated by the first electroninjector 121 a to the first radioisotope production apparatus Ma butinstead allows the electron beam to travel to the linear accelerator 122of the free electron laser. The second deflector 132 directs theelectron beam generated by the second electron injector 121 b to thesecond radioisotope production apparatus RI_(b).

The third radioisotope production apparatus RI_(c) is located after thelinear accelerator 122. The linear accelerator 122 is an energy recoverylinear accelerator, and provides an electron beam E_(R) from whichenergy has been recovered. This electron beam E_(R) has an energy whichsubstantially corresponds to the energy of the electron beam E providedfrom an electron injector 121 a,b before it is accelerated by the linearaccelerator 122. The energy of the electron beam as output from theelectron injector 121 a,b and following energy recovery in the linearaccelerator 122 may, for example, be around 10 MeV.

In common with the previously described radioisotope productionapparatus, the third radioisotope production apparatus RI comprises alinear accelerator 130 c which is configured to increase the energy ofthe electrons in the electron beam. The linear accelerator 130 c may,for example, accelerate electrons to an energy of 15 MeV or more. Thelinear accelerator 130 c may accelerate electrons to an energy of 30 MeVor more (e.g. up to around 45 MeV). In an embodiment, the linearaccelerator 130 c may accelerate electrons to an energy of around 35MeV. The radioisotope production apparatus further comprises a target140 c.

When radioisotope production is not required using the thirdradioisotope production apparatus RI_(c), the electron beam E_(R) isdirected to the beam dump 150 instead of being directed to the thirdradioisotope production apparatus. In FIG. 10 the electron beam isdirected to the beam dump 150 (as indicated by a solid line), and is notdirected to the third radioisotope production apparatus RI_(c) (asindicated by a dashed line). However, the electron beam E_(R) may bedirected by a deflector 133 towards the third radioisotope productionapparatus RI_(c). In an embodiment, the third radioisotope productionapparatus RI_(c) may be operative to produce radio isotopes at the sametime as the first (or second) radioisotope production apparatus RI_(a),RI_(b).

A merger (not shown) may be used to combine the electron beam providedby the electron injector 121 a,b with the recirculating electron beam E.A demerger (not shown) may be used to separate the electron beam E_(R)from which energy has been recovered and the electron beam E which hasbeen accelerated by the linear accelerator 122.

Although FIG. 10 shows radioisotope production apparatus RI_(a-c)located both before and after the linear accelerator 122 of the freeelectron laser FEL, in other embodiments the radioisotope productionapparatus may be provided in only one of those locations (i.e. providedonly before the linear accelerator or provided only after the linearaccelerator). More generally, it will be appreciated that FIG. 10 ismerely exemplary and that other arrangements may be provided. Forexample, in an embodiment, a single electron injector may be providedwith a single radioisotope production apparatus.

Although the embodiment illustrated in FIG. 10 is an energy recoverylinear accelerator, the radioisotope production apparatus may beprovided as part of a system which comprises a free electron laser FELwith an accelerator which is not an energy recovery linear accelerator.For example, radioisotope production apparatus may be provided after oneor more electron injectors of a free electron laser which comprises alinear accelerator that is not an energy recovery linear accelerator.

Although only a single linear accelerator 122 is depicted in FIG. 10,the free electron laser FEL may comprise two or more linearaccelerators. For example, a linear accelerator may be provided at theposition at which the undulator 124 is depicted in FIG. 10. Where thisis the case, the electron beam may pass through the linear acceleratorsa plurality of times such that the electron beam is accelerated by eachlinear accelerator two or more times. In such an arrangement, a beamde-merger may be used to separate the accelerated electron beam suchthat it passes through an undulator to generate an EUV radiation beam. Abeam merger may then be used to direct the electron beam from theundulator back into the linear accelerators for subsequent deceleration.

FIGS. 11a to 11h schematically depict exemplary targets 150 a-150 f,which may be used, for example, with any one of the radioisotopeproduction apparatuses shown in FIGS. 1, 4 and 10. FIGS. 11a, 11b, 11d,11f, and 11g show top views of the targets 150 a-150 e.

The targets 150 a-150 e shown in FIGS. 11a to 11g each comprises aplurality of spaced portions 151 a. Each of the targets 150 a-150 eshown in FIGS. 11a to 11g is configured to expand when the target issubjected to an electron beam E (only shown in FIG. 11f ) such thatcontact between the plurality of portions 151 a is prevented. Each ofthe targets 150 a-150 e may be configured to expand such that a gap orspace 151 b between adjacent portions of the plurality of portions 151 ais maintained.

Referring to FIGS. 11a to 11e , the targets 150 a to 150 c may eachcomprise a plurality of contact points 151 c at which adjacent portionsof the plurality of portions 151 a are in contact. The targets 150 a-150c may each comprise a plurality of openings 151 d arranged to extendbetween the at least two contact points of the plurality of contactpoints 151 c. The space or gap 151 b may be part of or comprised in theplurality of openings 151 d. The plurality of openings 151 d may beconfigured for receiving a flow of coolant there through.

The target 150 a shown in FIG. 11a comprises a flexible or deformabletarget 150 a. The target 150 a may be configured to expand in one or twodirections, for example when the target is subjected to the electronbeam E. For example, when the target 150 a is subjected to heat causedby the electron beam E, the target 150 a may freely expand, for examplein one or two directions, such as one or two substantially transversedirections, which are indicated as x- and y-directions in FIG. 11a .This may allow the target 150 a to expand, for example, when the target150 a is subjected to heat caused by the electron beam E, withoutblocking of the space or gap 151 b between adjacent portions of target.By preventing blocking of the space or gap 151 b between adjacentportions of the target 150 b, a coolant may be able to flow between theplurality of portions of the target 150 a and thus, overheating and/ormelting of the target 150 a may be prevented. The target 150 a is shownin FIG. 11a as comprising a lattice-type structure. It will beappreciated that in other embodiments the target may comprise or ahoneycomb structure or the plurality of openings may have a circular,squared or rectangular shape or the like.

Referring to FIGS. 11b to 11e , the plurality of portions 151 a of thetargets 150 b, 150 c may comprises a plurality of target elements 151 a.In the embodiments shown in FIGS. 11b and 11d the plurality of targetelements 151 a are arranged to form the target 150 b, 150 c. Forexample, the target elements 151 a may be stacked or joint together toform the target 150 b, 150 c. In the embodiment shown in FIGS. 11b and11c , each target element 151 a comprises a plurality of grooves. In theembodiments shown in FIGS. 11d and 11e each target element 151 acomprises plurality of through-holes 151 f. The plurality of grooves 151e or through-holes 151 f may be arranged in the target elements 151 a toprovide the plurality of openings 151 d and contact points 151 c, forexample, when the target elements 151 a are joint together to form thetarget 150 b, 150 c. The plurality of grooves 151 e may be provided inthe form of a plurality of corrugations. The plurality of through-holes151 f may be provided in the form of a plurality of punched holes. FIGS.11b and 11d each show a top view of three target elements 151 a joint toeach other. It will be appreciated that in other embodiments, there maybe provided more or less than three target elements.

The plurality of through-holes 151 f or corrugations 151 e in the targetplates 150 b, 150 c may lead to an increased transfer of heat, forexample, when the target 150 a, 150 c is subjected to heat caused by theelectron beam E. This may prevent blocking of the space 151 b betweenadjacent target elements 151 a and the coolant may be allowed to flowbetween the target elements 151 a. Therefore, overheating and/or meltingof the target 150 b, 150 c may be prevented.

The exemplary target 150 d shown in FIG. 11f comprises a plurality ofportions 151 a, which are concentrically arranged to each other. Theexemplary target 150 e shown in FIG. 11g comprises a plurality orportions 151 a, which are arranged to form a helical or spiralstructure. The concentric arrangement of the target 150 d and/or thespiral or helical structure of the target 150 e may allow the targets150 d, 150 e to freely expand, e.g. when each of targets is subjected toheat caused by the electron beam E, without blocking or obstructing thespace 151 b between adjacent portions 151 a of the targets 150 d, 150 e.Therefore, overheating and/or melting of the targets may be prevented.As shown in the top view of the exemplary target 150 d in FIG. 11f , theelectron beam E may be directed on the targets 150 d, 150 e in adirection substantially perpendicular to a central or longitudinal axisof the targets 150 d, 150 e.

FIG. 11h shows another exemplary target 150 f for use with aradioisotope production apparatus. The target 150 f is configured toexpand, for example, when the target is subjected to the electron beam Esuch that flow of a coolant through the target is allowed. The target150 f may comprise a porous structure or material. The porous structureor material may comprise a foam or sintered material. For example, whensubjected to heat caused by the electron beam E the porous structure ormaterial of the target 150 f may allow the target 150 f to internallydeform. Due to the porosity of the target 150 f, flow of coolant throughthe target 150 f may be maintained and overheating and/or melting of thetarget 150 f may be prevented.

FIGS. 12a and 12b show exemplary target arrangements 152 a, 152 b, whichmay be used, for example, with any one of the radioisotope productionapparatuses shown in FIGS. 1, 4 and 10. The target arrangements 152 a,152 b each comprise a target 153 a, 153 b and a target support 154 a,154 b. The target 153 a, 153 b may be or include any one of the targetsdescribed above. The target support 154 a, 154 b may be configured tomove or rotate the target 153 a, 153 b relative to the electron beam E.By configuring the target support 154 a, 154 b to rotate or move thetarget 153 a, 153 b relative to the electron beam E, uniform activationof the target 153 a, 153 b may be achieved, which may lead to anincreased radioisotope production. This may lead to a reduction of thethermal load on the target, e.g. a portion of the target. Alternativelyor additionally, by configuring the target support 154 a, 154 b torotate or move the target 153 a, 153 b relative to the electron beam E,it may be possible to direct the electron beam E onto the target 153 a,153 b from one side only. This may make the use of a beam splitter, e.g.a kicker, which splits the electron beam E along two propagation paths,as described above, and which may be a complex part, unnecessary.Alternatively or additionally, this may avoid the use of long beam linesand may reduce the amount of magnets and metrology required in such beamlines, which may lead to reduced beam line and/or radioisotopeproduction costs. Alternatively or additionally, the target support 154a, 154 b may be configured to moveably or rotatably mount the respectivetarget 153 a, 153 b, for example, to allow movement or rotation of thetarget 153 a, 153 b relative to the electron beam E.

The exemplary target support 154 a shown in FIG. 12a is configured tomove or rotate the target 153 a, for example, about a transverse axis A,e.g. an axis extending in a direction substantially perpendicular to alongitudinal axis of the target 153 a. The target support 154 a may beconfigured to rotate or move the target 153 a by 180 degrees, forexample, to allow for alternate exposure of each side of the target 153a to the electron beam E. It will be appreciated that in otherembodiments the target support may be configured to rotate or move thetarget about a longitudinal axis of the target.

The exemplary target support 154 b shown in FIG. 12b is configured torotate move of the target 153 b about a longitudinal axis B of thetarget 153 b. The exemplary target 153 b shown in FIG. 12b includes acylindrical target 153 b. It will be appreciated that in otherembodiments the target may have a different shape, such as squared orrectangular shape, and/or may include a plurality of target plate, whichmay be of a squared, circular, rectangular shape.

The exemplary target arrangements shown in FIGS. 12a and 12b may includean actuator (not shown), which may be provided in the form of a motor orthe like. The target 153 a, 153 b may be mounted on an axle defining theaxis A or axis B and the actuator may be coupled or connected to thetarget support 154 a, 154 b (or a portion thereof) to cause movement orrotation of the target 153 a, 153 b relative to the electron beam E. Itwill be appreciated that the target 153 a, 153 b may be caused to rotateor move about the axis A or axis B in any suitable manner. Further, itis to be understood that the axis A or axis B need not be centrallydisposed with the target 153 a, 153 b.

FIGS. 13a to 13c show exemplary target arrangements 155 a, 155 b, 155 c,which each include a housing 156 a, 156 b, 156 c and a window 157 a, 157b, 157 c for transmission of the electron beam E into the housing 156 a,156 b, 156 c.

In the exemplary target arrangements shown in FIGS. 13a and 13b , thetarget 153 b and/or target support 154 b may be arranged in the housing156 a, 156 b to move or rotate the target 153 b relative to the housing156 a, 156 b and the window 157 a, 157 b. For example, as shown in FIG.13b , an actuator, which may be provided in the form of a motor 158, maybe coupled or connected to the target support 154 b. The window 156 amay be considered as being fixed or stationary relative to the target153 b. This arrangement may allow the target 153 b to be subjected tothe electron beam E from one side only, while the activation of thetarget 153 b, e.g. of all target plates, may be the same or uniform. Inuse, the housing 155 a may be subjected to a higher dose of the electronbeam compared to the target 153 b. Although the window 156 a is shown inFIGS. 13a and 13b as having a rectangular shape, it will be appreciatedthat in other embodiments the shape of the window may be different. Forexample, the window may be provided in the form of a slit or may have asquared shape. The target support 154 b shown in FIG. 13b may be thesame or at least similar to that shown in FIG. 12b . It will beappreciated that in the embodiment shown in FIG. 13a the target support(not shown) may be provided in or by the housing 156 a.

In the exemplary target arrangement 155 c shown in FIG. 13c , the window157 b is arranged to surround the target 153 b. By arranging the window157 b to surround the target 153 b, the target 153 b may be exposed tothe electron beam E from more than one side. For example, the target 153b may be exposed to the electron beam E from two sides, e.g. twoopposing sides, or from three or more sides. In the embodiment shown inFIG. 13c , the housing 156 c comprises an upper portion 156 c′ and alower portion 156 c″. The window 157 c may be arranged between the upperand lower portions 156 c′, 156 c″ of the housing 156 c.

In the embodiment shown in FIG. 13c , the target support (not shown) isconfigured to move or rotate housing 156 c and/or the window 157 c withthe target 153 b. The housing 156 c may be part of the target supportand may be configured to rotate or move the window 157 c and target 153b relative to the electron beam E. This may lead to a reduced heat loadon the window 157 c and may allow uniform activation of the target 153b. In the exemplary target arrangement 155 c shown in FIG. 13c , thehousing 156 c, e.g. the lower portion 156 c″ of the housing 156 c iscoupled or connected to a motor 158 for moving or rotating the housing156 c, window 157 c and target 153 b.

Referring to FIGS. 13b and 13c , the target arrangement 155 b, 155 c maycomprise an inlet 159 a for supplying the coolant to the target 153 band an outlet 159 b for discharging coolant from the target 153 b. Theinlet 159 a and outlet 159 b may be part of the housing 156 b, 156 c.The coolant, which may be in the form of helium coolant, may also beprovided to cool the window 157 b, 157 c. This may be facilitated by aspace or gap 160 between the window 157 b, 157 c and the target 153 b.

FIGS. 14a and 14b schematically depict an exemplary radioisotopeproduction apparatus, which may comprise an electron beam focusingarrangement (not shown) configured to focus the electron beam E on thetarget 160. The target 160 may comprise any one of the targets describedabove and/or may be held by any one of the target supports describedabove. The electron beam focusing arrangement may comprise a lens (notshown), which may, for example, be formed from magnets, and may be amultipole (e.g. quadrupoles, hexapoles, octupoles) lens. In thisembodiment, the target 160 may be arranged to be fixed or stationaryrelative to the electron beam E. It will be appreciated that in otherembodiments, the target may be moved or rotated relative to the electronbeam, for example, as described above. By focusing the electron beamonto the target, a uniform heat load on the target may be achieved.

FIGS. 15a to 15c show another exemplary target arrangement 161 for usewith a radioisotope production apparatus. The target arrangement 161comprises a plurality of spaced target elements 162 and a target support163. The target support 163 may be configured to suspend a part of theplurality of target elements 162 to allow expansion of the part oftarget elements 162 in at least one direction. It will be appreciatedthat in other embodiments the target support may be configured tosuspend all of the plurality of target elements.

The target support 163 may comprise a plurality of support elements 163a, which may be arranged in series. Each support element 163 a may beconfigured to suspend a portion of the target elements 162, as shown inFIG. 15c . This may allow parts, e.g. one or more support elements 163a, of the target 161 to be removed for recovery of converted targetmaterial, e.g. radioisotope material. Each support element 163 a andassociated target elements 162 may define a comb-like or toothcomb-likeshape or structure, as shown in FIG. 15c . The target elements 162 maybe considered as extending from the target support 163, e.g. from eachsupport element 163, and/or may be considered as each comprising a freeend. By configuring the target support 163 (or each/the target supportelement(s) 163 a) to suspend at least a part of the target elements 162,expansion of the target elements in a substantially longitudinaldirection, which is indicated as a y-direction in FIG. 15c , of thetarget arrangement 161 may allowed. This may prevent built-up of thermalstresses in the target arrangement 161, which in turn, may allow anincrease of the current and/or current density of the electron beam andmay lead to an increased conversion of the target into radioisotopematerial.

FIG. 15b schematically depicts a bottom view of the arrangement of thetarget elements 162 on the target support 163. As can be seen in FIG.15b , the target elements 162 are arranged to be staggered in at leastone direction. The target elements 162 may be staggered such that theelectrons of the electron beam are prevented from travelling unimpededfrom one side of the target 161 to another side of the target 161. Thismay allow an increased radioisotope production. In at least one otherdirection, the target elements 162 may be arranged to be in line witheach other.

The target arrangement may be configured such that some of the targetelements are of the same size and as least some other target element areof different sizes. For example, the target elements 162 of some targetsupport element 163 a may be of the same size, while the target elements162 of other target support elements 163 are of different sizes, e.g.widths or lengths. This arrangement of target elements 162 may providethe staggered arrangement.

FIG. 15c schematically depicts a single target support element 163 acomprising associated target elements 162. A space or gap 164 may beprovided between adjacent target elements 162. The coolant may be flowin the space or gap 164 between adjacent target elements 162. The spaceor gap 164, e.g. a size of the space or gap, is selected to allow fordilation or expansion of the target elements 162 in at least one otherdirection. For example, the size or gap may be selected to allow fordilation or expansion of the target elements 162 in one or moresubstantially transverse direction(s). For example, one of thetransverse directions may be along the x-direction depicted in FIG. 15cand another of the transverse directions may be substantiallyperpendicular to the x- and y-directions depicted in FIG. 15c . A sizeof space or gap between adjacent target elements may be about 0.1 mm.For example, when a helium coolant pressure is increased from 60 bar(6000 kPa) to 100 bar (10000 kPa) the maximum temperature of the targetarrangement 161 may decrease to below 800° C., which is below, forexample, the recrystallization temperature of Molybdenum. Attemperatures below 800° C. the expansion or deformation of the targetelements 162 may be considered to be small and the target elements 162may not contact each other, when the target arrangement 161 is subjectedto heat caused by the electron beam. It will be appreciated that thesize of the space or gap between adjacent target elements may beselected depending on a pressure of coolant supplied to the target.

The target arrangement 161 may be manufactured by a 3-D printingtechnique, such as selective laser melting (SLM). The size of the targetelement 162 and/or the space 164 between adjacent target elements 162may be determined by manufacturing restrictions.

FIGS. 15a to 15c show all of the target elements 162 as being suspendedfrom the target support. It will be appreciated that in otherembodiments a part of the target element may be supported. For example,the target support may comprise a first portion for suspending one partof the target elements and a second portion for supporting a free end ofanother part of the target elements. The second portion may be arrangedto support the target elements on one or two opposing sides of thetarget arrangement.

Each of the targets described in FIGS. 11a to 15c may comprise a Mo-100target. However, it should be understood that the invention is notrestricted to such target material and that in other embodiments othertarget materials may be used, for example, as described below.

FIGS. 16a to 16e schematically depicts the flow of an exemplary methodfor producing a radioisotope. FIG. 16a schematically depicts anotherexemplary target for use with a radioisotope production apparatus. Theexemplary target 165 shown in FIG. 16a comprises a first material 166,which comprises a substrate material (not shown) for conversion into aradioisotope material and a second material 167. The second material 167is configured to retain converted substrate material. The secondmaterial 167 is arranged or arrangeable in the first material 166 toform the target 165. For example, the second material 167 may be mixedinto or interspersed in the first material 166. However, the first andsecond material may remain distinct materials. It will be appreciatedthat in other embodiments, the first material may be arranged in thesecond material.

The first and second materials 166, 167 may comprise differentmaterials, e.g. chemically different substances. A transition betweenthe first material 166 and the second material 167 may define a boundary168. The first material 166 and the second material 167 may be distinctmaterials and/or may be separated by the boundary 168.

The method comprises arranging the target 165 in the radioisotopeproduction apparatus (step A). The method comprises irradiating thetarget 165 with an electron beam E (not shown) (step B). The electronbeam E is configured to cause conversion of a part of the substratematerial into radioisotope material. The electron beam E is configuredto cause displacement of some of the converted source material into thesecond material 167. As described above, when electrons in the electronbeam E are incident on the target 165, photons are emitted. The photons169 emitted by the target 165 are schematically depicted in FIG. 16b aswavy arrows. When a photon is incident on a nucleus of the substratematerial, it causes a photonuclear reaction via which a neutron isejected from the nucleus. For example, the photon 169 is absorbed by thenucleus of the substrate material. This causes the nucleus of thesubstrate material to become excited. The excited nucleus returns to itsground-state or becomes de-excited by emission of the neutron 170. Thenucleus of the substrate material is thereby converted to a radioisotopenucleus 171. In some embodiments, the de-excitation or return to theground state of the nucleus may result in fission of an atom of thesubstrate material. When the photon 169 is incident on the nucleus, someor all of the momentum of the photon may be transferred on the nucleus.This may be referred to as nuclear recoil and may result in the nucleusand/or ejected neutron to be become displaced, for example, in the firstmaterial and/or into the second material 167. In other words, thenuclear recoil may cause a nucleus to become implanted into the secondmaterial 167. For example, a photon that causes the above describedphotonuclear reaction may have an energy between 10 MeV and 50 MeV. Asdescribed above, the energy of the photon may be dependent on the energyof the electrons in electron beam. The momentum p=E/c of the photon maybe completely absorbed by the nucleus on which the photon is incident.Due to the conservation of momentum the nucleus, which may have anatomic mass unit (AMU) of about 100, may receive kinetic energy

${E_{nucl} = \frac{p^{2}}{2M_{nucl}}},$

which may be between 0.5 keV and 15 keV, whereby M_(nucl) the mass ofthe nucleus. Some of the transferred momentum may remain with thenucleus after de-excitation by emission of the neutron. The neutronemitted from the excited nucleus may have a kinetic energy of E_(n)≅1Mev. Due to the conservation of momentum, the nucleus may have a recoilkinetic energy of:

$\begin{matrix}{{E_{{nucl}{(1)}} = {{E_{n}*\frac{M_{n}}{M_{nucl}}} \cong {10\mspace{14mu}{keV}}}},} & (1)\end{matrix}$

whereby M_(n) is the mass of the neutron. A nucleus with a kineticenergy of 10 keV may be displaced in the target by about 10 nm. Thisdisplacement or distance is indicated in FIG. 16c by L. The secondmaterial 167 may comprise a plurality of particles 167 a. Each particle167 a of the second material 167 may have a size or dimension, e.g. adiameter, of less than 1 μm. For example, each particle 167 a of thesecond material 167 may have a size or dimension of about 10 nm. Thismay allow the radioisotope nucleus 170 to become displaced from thesubstrate material into the second material 167, e.g. the particles 167a thereof. It will be appreciated that in other embodiments the firstmaterial may comprise a plurality of particles, which may each have asize or dimension, e.g. a diameter, of less than e.g. about 10 nm.Alternatively, both the first and second materials may compriseparticles, which may have a size or dimension of less than e.g. about 10nm. The displaced radioisotope nucleus 170 is indicated in FIG. 16c byreference numeral 172 and the displacement is indicated curved lines173. FIG. 16c shows that the emitted neutron 170 has been displaced intoparticles 167 a of the second material 167. The trajectory of theemitted neutron 171 in the first material 166 is indicated in FIG. 16cby straight lines 174. It will be appreciated that the interactionbetween the emitted neutron 171 and the first material 166 may be weak.

The method comprises separating at least part of the converted substratematerial, e.g. the radioisotope nucleus 172 or the radioisotopematerial, from the second material 167 (Step C). This step may includeseparating the first material 166 from the second material 167, prior toseparating the converted substrate material from the second material167. The first material 166 may be separated or removed from the secondmaterial 167, for example, by chemical or physical evaporation ormelting of the first material 166. FIG. 16d shows the remainingparticles 167 a of the second material and the displaced or implantedconverted substrate material, e.g. the radioisotope nuclei 172.Subsequently to Step C, the converted material, e.g. the radioisotopenuclei 172 or radioisotope, may be separated from the second material167 (Step D), as shown in FIG. 16e . For example, the second material167 may be etched so that only the radioisotope material remains.

The second material 167 may comprise a material that is chemically inertor at least stable. This may facilitate arranging of the first materialin the second material. The second material may comprise a material thatmay be produced in bulk at low costs. Exemplary materials that may beused as the second material comprise at least one of graphene particlesor flakes, carbon particles or nanostructures, e.g. nanotubes, metalparticles or nanostructure, e.g. metal nanowires, colloid or colloidsolution, e.g. a colloid solution of particles or nanoparticles, e.g. azeolite matrix, and alumina (e.g. aluminum oxide (Al₂O₃)) particles ornanostructure, e.g. alumina nanofibers. For example, the aluminananofibers may have a diameter of about 10 nm to 15 nm and may beproducible at any length, such as 10 cm or more. The exemplary aluminananofibers may comprise crystalline gamma-phase alumina fibers, whichmay have a surface area of about 155 m²/g, a tensile strength of 12 GPa,a tensile modulus of 400 GPa, a faceted surface with vacant aluminumbonds, a bulk density of 0.1-0.4 g/cm³, a thermal conductivity of about30 W/mK and/or may maintain gamma phase stability in temperatures up to1200° C. The exemplary alumina nanofibers may be configured to allowunidirectional fiber alignment, dispersion in resins and/or liquidsand/or to be fire resistant. The exemplary alumina fibers may compriseNAFEN alumina fibers.

An exemplary target 165 may be configured for the production ofDysprosium-157 (Dy-157), which has a half-life of 8 hours, fromDysprosium-158 (Dy-158), which may be considered as stable. Dy-157 may,for example, find utility in medical diagnostic methods, such as singlephoton emission computer tomography (SPECT). The target may be producedby mixing or arranging a salt of Dysprosium (e.g. DyC13) with aluminananofibers. The salt may occupy about 90% of the volume and the aluminananofibers may occupy about 10% of the volume. A distance between thealumina nanofibers, e.g. parallel alumina nanofibers, may range fromabout 20 nm to about 50 nm. As described above, the target 165 may beirradiated with an electron beam and emitted photons may be absorbed bythe target.

FIG. 17a illustrates the trajectories of Dysprosium ions having anenergy of 10 keV in a solid. The Dysprosium is displaced or implanted byabout 2 nm into layers of Dysprosium and by about 10 nm into the aluminananofibers (which is referred to as “sapphire” in FIGS. 17a and 17b ).FIG. 17b illustrates the distribution of the Dysprosium ions in theDysprosium and the alumina nanofibers. From FIG. 17b it can be seen thatthe maximum of the Dysprosium ion distribution lies in the nanofibers.FIG. 17c illustrates a chart of nuclides, whereby the x-axis indicatesthe number of neutrons in a nucleus and the y-axis indicates the numberof protons in a nucleus. From this chart can be seen that a large numberof Dy-157 radioisotope were produced. Stable isotopes are indicated byreference numeral 172 a in FIG. 17c . Radioisotopes that are deficientof neutrons correspond to isotopes that decay via positron emission orelectron capture are indicated by reference numeral 172 b in FIG. 17c .Subsequent to the irradiation of the target 165 with the electron beam,the salt may be removed and the alumina nanofibers may be etched, e.g.by using base solution, such as potassium hydroxide (KOH) or sodiumhydroxide (NaOH) solution. Once the alumina nanofibers have been etched,the Dy-157 radioisotopes may be extracted from the solution.

Another exemplary target 165 may be configured for the production ofRadium-224 (Ra-224), which is an alpha-emitter and has a half-life of3.7 days, from Radium-226 (Ra-226, which has a half-life of 1600 years.Ra-224 may, for example, find utility in medical diagnostic methods,such as targeted therapy of cancerous tissue or tumors. The methoddescribed above may be used to produce Ra-224 from Ra-226 and toseparate the Ra-224 isotopes from the carrier material. A by-product ofthe reaction (γ, 2n) may be Radium-225 (Ra-225), which may be producedin large amounts and may be used for SPECT imaging. By irradiating thetarget with the electron beam, as described above, the amount of fissionproducts may be reduced compared to the production of Ra-224 by protonbeam irradiation.

Another exemplary target 165 may be configured for the production ofRa-224 from Thorium-228 (Th-228), which has a half-life of 2 years. Afirst material comprising Thorium-232 (Th-232) may be mixed with aluminananofibers to form the target. The target may be irradiated by theelectron beam. The irradiation of the first material may be repeated. Asdescribed above, due to the photonuclear reaction (γ, 4n) of the Th-232with the photons, Th-230, Th-229, Th-228 and Protactinium-231 (Pa-231)may be produced. By repeating the irradiation of the target with theelectron beam, Ra-224 may be produced from Th-228. The Ra-224 isotopesmay then be separated from the alumina nanofibers, as described above.This may allow the Ra-224 to be separated from Thorium by using areduced amount of chemicals, than that needed in other methods.

Another exemplary target may be configured for the production ofNickel-63 from Nickel-64, which may be stable. Ni-63 may, for example,find utility in electric high-power supply devices, such as beta-decaydriven (beta voltaic) batteries for embedded electronics. The provisionof Ni-63 may allow the manufacture of miniaturized power supply devices,which may have a 100 year lifetime. The first material comprising Ni-64may be mixed with second material to form the target. The target may beirradiated with the electron beam and due to the photonuclear reaction(γ, n) of the Ni-64 with the photons, Ni-63 may be produced. Asdescribed above, the Ni-63 may be separated from the carrier material.The exemplary method disclosed herein may be considered as analternative method for the production of Ni-63, which may not rely onthe use of reactors, such as high-flux neutron reactors or the like.Alternatively or additionally, the yield of Ni-63 may be increasedcompared to the yield of Ni-63 from a reactor.

Although the above exemplary method for producing a radioisotope hasbeen described as comprising the irradiation of the target with anelectron beam, it will be appreciated that in other embodiments, thetarget may be irradiated with a proton, deuteron or ion beam. Theirradiation of the target with such beam may cause an increaseddisplacement of the radioisotopes in the second material. However, someatoms of the source material may be displaced into the second materialwithout a photonuclear reaction taking place.

Although in the above described exemplary method a neutron was ejectedfrom the nucleus, as a result of the photonuclear reaction, it will beappreciated that in other embodiments, a different photonuclear reactionmay cause ejection of a proton or alpha-particle from the nucleus. Insome embodiments, the different photonuclear reaction may result infission products. It should be understood that the above describedmethod may be used for the production of a nucleus or fission productresulting from the different photonuclear reaction.

FIGS. 18, 19 and 21 schematically depict another target arrangement 175,which may be used with a radioisotope production apparatus. The targetarrangement comprises a target 176, which may comprise a plurality oftarget plates 176 a. The target 176 is held by a support structure (notshown). The target 176 is mounted in a chamber 177. The chamber 177comprises a separation element 178, which separates the chamber 177 fromthe electron injector and electron source (not shown). The separationelement 178 may define a portion, e.g. a side wall, of the chamber 177.The separation element 178 comprises an aperture 179 through which theelectron beam E can enter the chamber 177. By allowing the electron beamto enter the chamber through the aperture in the separation element, theheat load, which may be caused by the electron beam, on the separationelement may be reduced. This may lead to an increased lifetime of theseparation element. The target arrangements shown in FIGS. 18, 19 and 21may be considered as “window-less” target arrangements. The describedseparation element may be considered as replacing a window that may beused to isolate the target from the electron beam environment.

The separation element 178 may be provided with the aperture 179 toreduce a pressure differential between the target 176 and the electronbeam environment 180, e.g. the electron injector (not shown) and/or theelectron accelerator (not shown) or respective portions thereof. Asdescribed above, the target 176 may be cooled, for example, with a gascoolant. In the example shown in FIGS. 18, 19 and 21, the target 176 iscooled by a flow of helium (He) 176 b. For example, helium coolant 176 bmay be supplied to the target 176 at a pressure of about 75 bar (7500kPa). The separation element 178 may be arranged in the chamber 177 suchas to allow flow of the helium coolant 176 b through the aperture 179into electron beam environment 180. This may lead to an increase of thepressure in the electron beam environment 180. For example, the pressureof the electron beam environment 180 may range from vacuum to 1 bar ofhelium. The flow of helium coolant 176 b through the aperture 179 mayallow a pressure differential between the target 176 or the chamber 177and the electron beam environment 180 to be decreased. This may preventdamages to the separation element, e.g. rupture of the separationelement 178, due to the pressure differential between the target orchamber 177 and the electron beam environment 180. Consequently, therisk of contamination to the electron beam environment due to rupture ofthe separation element may be reduced. One or more pumping or suctiondevice(s) 181, e.g. one or more differential pump(s) and/or a boosterpump, may be provided to minimize the pressure in the electron beamenvironment.

The chamber 177 may comprise an electron beam steering section 182,which may be arranged between the separation element 178 and the target176. In the electron beam steering section 182 the electron beam may bedefocused to enlarge the beam to a desired dimension for irradiation ofthe target 176, for example, by using a lens formed from magnets 182 a,as shown in FIG. 21. The helium coolant 176 b may be supplied to theelectron beam steering section 182 at a pressure of 70 bar (7000 kPa).This may lead to a reduction of the energy of the electron beam due toelectrons of the electron beam colliding with helium atoms. For anelectron beam having an energy of about 60 MeV, the reduction of theenergy of the electron beam may be about 3 MeV at a helium pressure ofabout 70 bar (7000 kPa). This reduction in energy may be considered tobe acceptable. Due to the helium pressure in the beam steering sectioncooling of the chamber 177 and/or the target 176 may be provided.

The size or diameter of the aperture 179 in the separation element maybe selected dependent on a size, e.g. collimation, of the electron beamE. For example, the size of the electron beam may be below 0.1 mm, inwhich case the size or diameter of the aperture may be about 1 mm. For ahelium pressure of, for example, 70 bar (7000 kPa) in the electron beamsteering section 182, this size may result in a flow rate of the heliumcoolant 176 b through the aperture 179 of about 0.005 kg/s. If the sizeof the aperture 179 is increased to 2 mm, then the helium coolant flowrate through the aperture may be about 0.02 kg/s. The aperture 179 maybe considered as a critical flow restriction.

In the exemplary target arrangement 175 shown in FIG. 19, the chamber177 may additionally comprise a shielding element, which may be providedin the form of a shielding plate 183. The shielding plate 183 maycomprise an aperture 184 through which the electron beam E passes to thetarget 176. The shielding plate 183 may be arranged between theseparation element 178 and the target 176. The aperture 184 of theshielding plate may be larger than the aperture 179 of the separationelement 178. For example, the aperture 184 of the shielding plate 183may have a size or diameter of about 20 mm. Due to the aperture 179 inthe separation element 178, a pressure differential may act across thetarget 176, e.g. a first plate 176 a of the target 176. The first plateof the target 176 may be arranged to be proximal to the separationelement 178. By arranging the shielding plate 183 in the chamber 177,the pressure differential acting on the target 176, e.g. the first plateof the target 176, may be reduced. The shielding plate 183 may bearranged to balance the helium coolant 176 b flow from the target 176 tothe electron beam environment 180 through the aperture 179 of theseparation plate 178. The chamber 177 may comprise a portion 185, whichextends between the shielding plate 183 and the target 176. The portion185 of the chamber may be supplied with helium coolant 176 b, forexample, at the same pressure as the helium pressure supplied to thetarget 176. By supplying the portion 185 of the chamber 177 with heliumcoolant 176 b at the same pressure as the helium pressure supplied tothe target, cooling of the target 176 may be increased.

FIGS. 20a to 20c schematically depict the helium coolant 176 b flow inthe chamber 177 between the separation element 178 and the shieldingplate 183 and between the shielding plate 183 and the target 176. Thehelium coolant 176 b flow between the separation element 178 and theshielding plate 183 and/or between the shielding plate 183 and thetarget 176 may be adjusted to create a pressure profile in the portion185 of the chamber 177, which may be similar to a pressure profile atthe target 176.

The radioisotope production apparatus may comprise a cooling apparatus(not shown). The cooling apparatus may be configured to provide thehelium coolant 176 b to the target 176 and/or chamber 177, as describedabove. In the example of FIG. 20a , the cooling apparatus may beconfigured to provide the helium coolant 176 b to the portion 185 of thechamber 177 and/or to extract the helium coolant 176 b from the portion185. The cooling apparatus may be configured to supply the portion 185with helium coolant 176 b at a pressure of 75 bar (7500 kPa). Heliumcoolant extracted from the target 176 and/or the portion 185, forexample, by the cooling apparatus may have a pressure of about 65 bar(6500 kPa).

In the example of FIG. 20b , the cooling apparatus may be configured toadditionally supply helium coolant 176 b to a further portion 186 of thechamber 177. The further portion may extend between the separationelement 178 and the shielding plate 183. The cooling apparatus maysupply the further portion 186 with helium coolant 176 b, for example,at a pressure of 70 bar (7000 kPa). The further portion may be part ofor comprised in the electron beam steering section 182 or a partthereof.

In the example of FIG. 20c , the cooling apparatus may be configured toadditionally supply helium coolant 176 b to a further portion 186 of thechamber 177 and to extract the helium coolant 176 b from the furtherportion 186.

FIG. 21 schematically depicts another example of the target arrangement175. The target arrangement depicted in FIG. 21 is similar to thatdepicted in FIG. 18. However, in the example depicted in FIG. 21, thechamber 177 comprises a further separation element 187. The furtherseparation element 187 may comprise a further aperture 188. The furtheraperture 188 of the further separation element 187 may be of the samesize or of a different size than the aperture 179 of the separationelement 178. By arranging a further separation element comprising afurther aperture, the helium coolant 176 b flow to the electron beamenvironment 180 may be reduced.

In an embodiment, a system comprising a free electron laser and aradioisotope production apparatus may be configured to provide anelectron beam with a current of 10 mA or more. The current provided bythe system may, for example, be 20 mA or more or may be 30 mA or more.The current may, for example, be up to 100 mA or more. An electron beamwith a high current (e.g. 10 mA or more) is advantageous because itincreases the specific activity of the radioisotope produced by theradioisotope production apparatus.

As explained further above, Mo-100 may be converted to Mo-99 (a desiredradioisotope) using very hard X-ray photons generated by an electronbeam hitting an electron target. The half life of Mo-99 is 66 hours. Asa consequence of this half-life there is a limit to the specificactivity of Mo-99 which can be provided when starting with Mo-100, thelimit being determined by the rate at which Mo-99 is generated. If theMo-99 is generated at a relatively low rate, for example using anelectron beam current of around 1-3 mA, then it may not be possible toprovide a specific activity of more than around 40 Ci/g of Mo-99 in thetarget. This is because although the irradiation time may be increasedin order to allow generation of more Mo-99 atoms, a significantproportion of those atoms will decay during the irradiation time. Thethreshold of specific activity of Mo-99 used in medical applications inEurope should be 100 Ci/g, and thus Mo-99 with a specific activity of 40Ci/g or less is not useful.

When a higher electron beam current is used the rate at which Mo-99atoms are generated is increased accordingly (assuming that the volumeof Mo-99 which receives photons remains the same). Thus, for example,for a given volume of Mo-99, an electron beam current of 10 mA willgenerate Mo-99 at 10 times the rate of generation provided by anelectron beam current of 1 mA. The electron beam current used byembodiments of the invention may be sufficiently high that a specificactivity of Mo-99 in excess of 100 Ci/g is achieved. For example, anembodiment of the invention may provide an electron beam with a beamcurrent of around 30 mA. Simulations indicate that, for a beam currentof around 30 mA, if the electron beam has an energy of around 35 MeV andthe volume of the Mo-100 target is around 5000 mm³ then a specificactivity of Mo-99 in excess of 100 Ci/g can be obtained. The Mo-100target may for example comprise 20 plates with a diameter of around 25mm and a thickness of around 0.5 mm. Other numbers of plates, which mayhave non-circular shapes and may have other thicknesses, may be used.

As noted further above, an electron injector of an embodiment of theinvention may be a photo-cathode which is illuminated by a pulsed laserbeam. The laser may, for example, comprise a Nd:YAG laser together withassociated optical amplifiers. The laser may be configured to generatepicosecond laser pulses. The current of the electron beam may beadjusted by adjusting the power of the pulsed laser beam. For example,increasing the power of the pulsed laser beam will increase the numberof electrons emitted from the photo-cathode and thereby increase theelectron beam current.

The electron beam received by a radioisotope production apparatusaccording to an embodiment of the invention may, for example, have adiameter of 1 mm and a divergence of 1 mrad. Increasing the current inthe electron beam will tend to cause the electrons to spread out due tospace charge effects, and thus may increase the diameter of the electronbeam. Increasing the current of the electron beam may therefore reducethe brightness of the electron beam. However, the radioisotopeproduction apparatus does not require an electron beam with, forexample, a diameter of 1 mm and may utilize an electron beam with agreater diameter. Thus, increasing the current of the electron beam maynot reduce the brightness of the beam to such an extent thatradioisotope production is significantly negatively affected. Indeed,providing the electron beam with a diameter greater than 1 mm may beadvantageous because it spreads the thermal load delivered by theelectron beam. It will be appreciated, however, that other injectortypes may also be used.

Although embodiments of the invention have been described in connectionwith generation of the radioisotope Mo-99, embodiments of the inventionmay be used to generate other radioisotopes. In general, embodiments ofthe invention may be used to generate any radioisotope which may beformed via direction of very hard X-rays onto a source material.

An advantage of the invention is that it provides production ofradioisotopes without requiring the use of a high flux nuclear reactor.A further advantage is that it does not require the use of highlyenriched uranium (a dangerous material which is subject tonon-proliferation rules).

Providing the radioisotope production apparatus as part of a systemwhich also comprises a free electron laser is advantageous because itutilizes apparatus already required by the free electron laser. That is,the radioisotope production uses apparatus which is, in part, alreadyprovided. Similarly, the radioisotope production apparatus may belocated in an underground space (which may be referred to as a bunker)which includes shielding that contains radiation and prevents it fromspreading to the environment. The underground space and at least some ofthe shielding may already be provided as part of the free electronlaser, and thus the expense of providing an entirely separateunderground space and associated shielding for the radioisotopeproduction apparatus is avoided.

In an embodiment, a system may comprise a free electron laser and aradioisotope production apparatus which are capable of operatingindependently of each other. For example, the free electron laser may becapable of operating without the radioisotope production apparatusoperating, and the radioisotope production apparatus may be capable ofoperating without the free electron laser operating. The free electronlaser and radioisotope production apparatus may be provided in a commonbunker.

Whilst embodiments of a radiation source SO have been described anddepicted as comprising a free electron laser FEL, it should beappreciated that a radiation source may comprise any number of freeelectron lasers FEL. For example, a radiation source may comprise morethan one free electron laser FEL. For example, two free electron lasersmay be arranged to provide EUV radiation to a plurality of lithographicapparatus. This is to allow for some redundancy. This may allow one freeelectron laser to be used when the other free electron laser is beingrepaired or undergoing maintenance.

Although embodiments of the invention have been described as usingMo-100 to generate Mo-99 radioisotope which decays to Tc-99, othermedically useful radioisotopes may be generated using embodiments of theinvention. For example, embodiments of the invention may be used togenerate Ge-68, which decays to Ga-68. Embodiments of the invention maybe used to generate W-188, which decays to Re-188. Embodiments of theinvention may be used to generate Ac-225, which decays to Bi-213, Sc-47,Cu-64, Pd-103, Rh-103m, In-111, I-123, Sm-153, Er-169 and Re-186.

It is to be understood that embodiments depicted in FIGS. 1 to 9 and 11a to 21 above may be combined in any suitable combination as will beapparent to the skilled person from the teaching above. For example, itis described with reference to FIGS. 1 and 3 that two electron targetsmay be provided either side of a photon target. It is to be understoodthat this arrangement may be combined with other described arrangements,such as those described with reference to FIGS. 1, and 5 to 8.

A lithographic system LS, such that that depicted in FIG. 10, maycomprise any number of lithographic apparatus. The number oflithographic apparatus which form a lithographic system LS may, forexample, depend on the amount of radiation which is output from aradiation source SO and on the amount of radiation which is lost in abeam delivery system BDS. The number of lithographic apparatus whichform a lithographic system LS may additionally or alternatively dependon the layout of a lithographic system LS and/or the layout of aplurality of lithographic systems LS.

Embodiments of a lithographic system LS may also include one or moremask inspection apparatus MIA and/or one or more Aerial InspectionMeasurement Systems (AIMS). In some embodiments, the lithographic systemLS may comprise a plurality of mask inspection apparatuses to allow forsome redundancy. This may allow one mask inspection apparatus to be usedwhen another mask inspection apparatus is being repaired or undergoingmaintenance. Thus, one mask inspection apparatus is always available foruse. A mask inspection apparatus may use a lower power radiation beamthan a lithographic apparatus. Further, it will be appreciated thatradiation generated using a free electron laser FEL of the typedescribed herein may be used for applications other than lithography orlithography related applications.

It will be further appreciated that a free electron laser comprising anundulator as described above may be used as a radiation source for anumber of uses, including, but not limited to, lithography.

The term “relativistic electrons” should be interpreted to meanelectrons which have relativistic energies. An electron may beconsidered to have a relativistic energy when its kinetic energy iscomparable to or greater than its rest mass energy (511 keV in naturalunits). In practice a particle accelerator which forms part of a freeelectron laser may accelerate electrons to energies which are muchgreater than its rest mass energy. For example a particle acceleratormay accelerate electrons to energies of >10 MeV, >100 MeV, >1 GeV ormore.

Embodiments of the invention have been described in the context of afree electron laser FEL which outputs an EUV radiation beam. However afree electron laser FEL may be configured to output radiation having anywavelength. Some embodiments of the invention may therefore comprise afree electron which outputs a radiation beam which is not an EUVradiation beam.

The term “EUV radiation” may be considered to encompass electromagneticradiation having a wavelength within the range of 4-20 nm, for examplewithin the range of 13-14 nm. EUV radiation may have a wavelength ofless than 10 nm, for example within the range of 4-10 nm such as 6.7 nmor 6.8 nm.

The lithographic apparatuses LA_(a) to LA_(n) may be used in themanufacture of ICs. Alternatively, the lithographic apparatuses LA_(a)to LA_(n) described herein may have other applications. Possible otherapplications include the manufacture of integrated optical systems,guidance and detection patterns for magnetic domain memories, flat-paneldisplays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.

Different embodiments may be combined with each other. Features ofembodiments may be combined with features of other embodiments. Further,it will be appreciated that while embodiments described above refer tolithography and in particular lithography using free electron lasers,the invention is not limited to such embodiments and that radioisotopesmay be generated in accordance with the embodiments of the invention inany free electron laser having a sufficient beam energy.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The descriptions above are intended to beillustrative, not limiting. Thus it will be apparent to one skilled inthe art that modifications may be made to the invention as describedwithout departing from the scope of the claims set out below.

1. A radioisotope production apparatus comprising: an electron sourceconfigured to provide an electron beam, the electron source comprisingan electron injector and an electron accelerator; a target supportstructure configured to support a target; and a first and a secondelectron beam distribution apparatus, together configured to scan theelectron beam over a surface of the target, wherein the radioisotopeproduction apparatus is configured to produce radioisotope materialbased on irradiating the target using the electron beam.
 2. Theradioisotope production apparatus of claim 1, wherein the first electronbeam distribution apparatus comprises a deflector configured to sweepthe electron beam through a predetermined angle towards the secondelectron beam distribution apparatus.
 3. The radioisotope productionapparatus of claim 2, wherein the deflector is further configured todeflect the electron beam by applying a magnetic or electric field tothe electron beam.
 4. The radioisotope production apparatus of claim 1,wherein the second electron beam distribution apparatus comprises adeflector or a lens.
 5. The radioisotope production apparatus of claim4, wherein the deflector is configured to direct the electron beamtoward the target telecentrically or the lens is configured to collimatethe electron beam.
 6. The radioisotope production apparatus of claim 1,further comprising a beam splitter configured to direct a first portionof the electron beam along a first path towards a first side of thetarget and to direct a second portion of the electron beam along asecond path towards a second side of the target.
 7. The radioisotopeproduction apparatus of claim 6, wherein the first and second electronbeam distribution apparatuses are disposed along the first path.
 8. Theradioisotope production apparatus of claim 7, further comprising thirdand fourth electron beam distribution apparatuses together configured toscan the electron beam over a further surface of the target, the thirdand fourth electron beam distribution apparatuses disposed along thesecond path.
 9. The radioisotope production apparatus of claim 1,wherein: the target comprises an electron target and a photon target;and the electron target is configured to receive the electron beam fromthe second electron beam distribution apparatus and to emit photonstowards the photon target.
 10. The radioisotope production apparatus ofclaim 8, wherein: the target comprises an electron target and a photontarget; the electron target is configured to receive the electron beamfrom the second electron beam distribution apparatus and to emit photonstowards the photon target; and the electron target comprises a firstpart configured to receive the first portion of the electron beam fromthe first and second electron beam distribution apparatuses and a secondpart configured to receive the second portion of the electron beam fromthe third and fourth electron beam distribution apparatuses.
 11. Theradioisotope production apparatus of claim 1, wherein the electronsource is a free electron laser.
 12. A method comprising: generating anelectron beam using an electron injector and an electron accelerator;supporting a target on a target support structure; scanning the electronbeam over a surface of the target using first and second electron beamdistribution apparatuses; and producing radioisotope material based onirradiating the target using the electron beam.
 13. The method of claim12, wherein: the first electron beam distribution apparatus comprises adeflector; and the method further comprises sweeping the electron beamthrough a predetermined angle toward the second electron beamdistribution apparatus using the deflector.
 14. The method of claim 13,further comprising deflecting the electron beam by applying a magneticor electric field to the electron beam.
 15. The method of claim 12,wherein: the second electron beam distribution apparatus comprises adeflector or a lens; and the method further comprises: directing theelectron beam toward the target telecentrically; or collimating theelectron beam.
 16. The method of claim 12, further comprising splittingthe electron beam to direct a first portion of the electron beam along afirst path towards a first side of the target and to direct a secondportion of the electron beam along a second path towards a second sideof the target.
 17. The method of claim 16, further comprising scanningthe electron beam over a further surface of the target using third andfourth electron beam distribution apparatuses disposed along the secondpath, wherein the first and second electron beam distributionapparatuses are disposed along the first path.
 18. The method of claim17, wherein the target comprises an electron target and a photon targetand the method further comprises: receiving the electron beam from thesecond electron beam distribution apparatus at the electron target;emitting photons from the electron target toward the photon target;receiving the first portion of the electron beam from the first andsecond electron beam distribution apparatuses at a first part of theelectron target; and receiving the second portion of the electron beamfrom the third and fourth electron beam distribution apparatuses at asecond part of the electron target.
 19. The method of claim 12, whereinthe target comprises an electron target and a photon target and themethod further comprises: receiving the electron beam from the secondelectron beam distribution apparatus at the electron target; andemitting photons from the electron target toward the photon target. 20.A lithographic system comprising: a free electron laser configured togenerate an electron beam and an illumination beam, the free electronlaser comprising an electron injector and an electron accelerator; alithographic apparatus configured to a project pattern onto a substrateusing the illumination beam; and a radioisotope production apparatusconfigured to produce radioisotope material based on irradiating thetarget using the electron beam, the radioisotope production apparatuscomprising: a target support structure configured to support a target;and a first and a second electron beam distribution apparatus, togetherconfigured to scan the electron beam over a surface of the target.